1. Field of Invention
This invention relates generally to improvements in the manufacture of ramp modules for ramp reaction plates adapted to interface with weight and roller centrifugal modules of automatic centrifugal clutches. More particularly, the invention relates to improvements in ramp modules affixed to ramp reaction plates, and commensurately to improved operation of vehicular clutches.
2. Description of the Prior Art
Automatically actuated centrifugal clutches include actuation modules of the type including centrifugal weights affixed to vehicular clutch covers. The weights are radially movable against spring loads as a function of engine speed. Several issues work against ideal operation of the modules over the useful lives of the clutches. For example, individually machined ramp units normally formed on and integral to the ramp reaction plates require very close manufacturing tolerances for each individual ramp profile. The process is expensive, slow, and works against achievement of manufacturing efficiencies.
In addition, the existence of tolerance variations in profile ramp angles creates nonuniform movements of the centrifugal mass weight rollers, giving rise to uneven performance of the centrifugal module during clutch actuation. As a result, the centrifugal module is vibration prone in one aspect of its less than satisfactory operation. In addition, to the extent that the tolerance variations limit proper interaction of the mass weight rollers and ramp reaction plate reaction modules during actuation, the overall efficiency and performance of the clutch actuation module suffers.
The present invention facilitates improved operation of a centrifugal actuation module in a centrifugally actuated vehicular clutch. In the described embodiment, a clutch ramp reaction plate is positioned adjacent the centrifugal actuation module. The ramp reaction plate is manufactured apart from individually machined ramp segments that are separately attached to the ramp reaction plate. In one embodiment, the ramp segments are made from a powdered metal process to assure that the tolerances are uniform from one ramp segment to the next. In an alternate embodiment, the ramp segments are formed of a hardened stamped steel material. The ramp reaction plate is machined to accept the segments. The segments include surface hardnesses that are higher than that of the ramp reaction plate to accommodate wear resistance.
The use of separate manufacturing processes for the ramp segments assures that they can be hardened in bulk from a harder material than that of the ramp reaction plate. In addition, the powdered metal ramp segments can be impregnated with lubricants or polytetrafluoroethylene materials to reduce rolling friction and wear between the ramp surfaces and the mass weight actuated rollers interacting with the surfaces.
The segments are attached to the ramp reaction plate by means of various fasteners including bolts, rivets, or adhesives. In one described embodiment, a special lip permits the strength requirement of the fastener to be reduced to the extent that the lip is adapted to resist centrifugal forces acting on the segment. Use of separately manufactured segments substantially reduces manufacturing costs, and assures higher product quality with lower tolerance variations.